1. Field of the Invention
The present invention relates to an engine control apparatus for an internal combustion engine, and more particularly to an improvement of an engine control apparatus which has two computing means, one for main engine control signals and the other redundantly provided for auxiliary engine control signals, in which switching from the main to the auxiliary engine control signals is made when the computing means for the main engine contol signals is not properly operating.
2. Description of the Related Art
A conventional apparatus of such a kind as described above is known from U.S. Pat. No. 4,444,048, for example. In the known apparatus, a main computer furnishes main control signals for an internal combustion engine to initiate a predetermined operation, in accordance with the engine operating parameters then sensed by various sensors which are installed in the engine and peripheral devices and equipment thereof, and an auxiliary computer operates only upon malfunction of the main computer and furnishes auxiliary control signals for the engine, i.e. signals which are simple so as to allow the minimum operation of the engine until such time as the next repair station can be reached.
There is further provided a switching circuit, whereby switching from the main to the auxiliary computer takes place if any error or malfunction in the main computer occurs. For this purpose, the main computer provides a monitoring signal as well as the main engine contol signals. The monitoring signal is a signal which indicates whether or not the main computer is properly operating. An error detector always monitors the monitoring signal, and outputs a switching signal to the switching circuit when the error detector detects an error, e.g., the absence of the monitoring signal indicative of correct operation of the main computer. Further, the auxiliary computer is monitored by means of a test program executed within the main computer.
In this way, in the known system the main computer is monitored by the error detector and the auxiliary computer is monitored by the main computer. However, no consideration is given to failure of the error detector itself, so that the reliability of the system as a whole is reduced. Further, in the known system, the error detectors of various kinds are composed of so-called wired logic circuits. As a result, the error detector is relatively complicated in its structure and lacks the flexibility to variation of the engine control.